1. Field of the Invention
This invention relates to a digital signal processing apparatus and more particularly to an apparatus for receiving analog signals which represent digital information and which processes such analog signals with high precision.
2. Description of the Related Art
In the field of magnetic recording and reproduction, a magnetic recording medium, in which a digital recording format suitable for consumer electronics, has been developed and is being manufactured.
In order to reproduce a digital signal which is based on this digital recording format, it is necessary, by means of rotary heads, to trace oblique tracks formed on a magnetic recording tape.
In the reproducing system of this type of apparatus, a signal to be reproduced is in analog form but contains digital information. Accordingly, the reproduced analog signal must be restored to digital form. In order to do this, it is necessary to provide: automatic gain control (AGC) to control the gain of the reproduced signal; automatic phase control (APC) to generate clock signals which are synchronized with the reproduced signal; and automatic tracking finding (ATF) for controlling tracking based on a reproduced pilot signal.
Since the digital information which is recovered in such apparatus will be processed in a digital manner, the above mentioned AGC, APC and ATF should also be obtainable in a digital manner in order to keep the system simple.
The prior art includes several techniques for obtaining the foregoing AGC, APC and ATF. In these techniques, a reproduced analog signal is transformed to a digital form. Also, phase detection for APC and gain detection for AGC, etc., are carried out or executed by processing of the digital information.
However, time or temperature changes may produce direct current offset components, which can become added to the output of the AGC and introduce errors in the detection process. In such a case, it becomes impossible to execute the above mentioned AGC, APC and ATF exactly.
Also, if the AGC circuit were to be made independent of the APC and the ATF circuits, the overall size of the circuits would be too large.
Accordingly, it is desired to provide small size circuits which are capable of correctly executing AGC, APC and ATF and which can be incorporated in Large Scale Integrated (LSI) circuits.